Record carrier with a follow-on track and apparatus for recording information thereon

ABSTRACT

An apparatus for recording information on a disk-shaped record carrier body by a beam of radiation. The carrier body comprises a diffractive follow-on track which is capable of being scanned with an opto-electronic system so as to produce an electrical signal for controlling the position of the beam during recording of the information.

This is a continuation of application Ser. No. 499,571, U.S. Pat. No.4,807,209, filed 5/31/83 which is a continuation of abandonedapplication Ser. No. 318,169 filed 11/4/81 which is a continuation ofabandoned application Ser. No. 127,354 filed 3/5/80 which is acontinuation of abandoned application Ser. No. 902,713 filed 5/4/78which is a continuation of abandoned application Ser. No. 619,039 filed10/2/75 which is a continuation of abandoned application Ser. No.431,422 filed 1/7/74.

The invention relates to a disk-shaped record carrier body, intended tobe provided with information, for example video and/oraudio-information, in an optically readable form. The record body has asubstantially information-free follow-on track on the surface thereof onwhich the information is to be stored. The follow-on track is intendedto be optically scanned and, in conjunction with an opto-electronicsystem, to produce an electric signal which is suitable for causing awrite beam to automatically follow the follow-on track.

The record carrier body is intended to be written on by a device whichsubstantially corresponds to that for reading a record carrier. A"record carrier" as used herein is to be understood to mean a recordcarrier body provided with information. If required, in the read devicean additional (write) radiation source as well as a modulation devicewhich is controlled by the information to be written, are included so asto permit a user, in addition to reading a pre-recorded record carrier,to record information on the record carrier body.

As used herein "information" is to be understood to mean that which isreproduced when reading the record carrier.

The opto-electronic device, which in the read apparatus is used fordetermining the position of the read beam relative to the track to beread during reading, may also be used to ensure that during informationwriting, the write beam accurately follows the track provided on therecord carrier body, hereinafter referred to as a "follow-on track" forthe sake of brevity. The follow-on track can be optically discriminatedfrom the rest of the record carrier body by making said track V-shapedand pressing it in the surface of the record carrier body, as describedin German Patent Application No. 2,038,874. The V-shaped groove causes abeam of radiation to be split into two sub-beams, the intensities of thesub-beams being defined by the degree of centering of the radiation beamrelative to the groove.

It is an object of the invention to indicate other possibilities ofoptically discriminating the follow-on track. The record carrier bodyaccording to the invention is characterized in that the follow-on trackis a flat track, and that the follow-on track influences the directionof a radiation beam in the same way as, but the radiation distributionover a beam section in a different way, than the rest of the surface ofthe record carrier body on which the information is to be written.

If the information recorded in the material can be read-out after a timeinterval of the order of the duration of one revolution of the recordcarrier body after it has been written, it suffices according to theinvention if the follow-on track extends over a relatively small part ofthe information surface as long as it is describes at least one fullrevolution on said surface.

It is to be noted that it is known from U.S. Pat. No. 3,391,255 to use afollow-on track which is located in one plane and which has anabsorption coefficient which differs from its surrounding for writing onan information-carrier body. However, the follow-on track is then notprovided on the write surface of the record carrier body, but on anadditional disk. This imposes strict requirements on the bearing of thedisk and on the synchronism of the movements. Moreover, a fairlyintricate set-up is required.

The invention will now be described in more detail, inter alia withreference to the drawing, in which an embodiment is shown of a deviceaccording to the invention for writing on a record carrier body, as wellas for reading a record carrier provided with information.

The follow-on track may be provided at the surface of the record carrierbody in different forms. For example, the reflection coefficient or theabsorption coefficient of the follow-on track may differ from itssurrounding, so that the intensity of a beam which emerges from therecord-carrier body differs according to whether the beam has or has notinteracted with the track. However, it is also possible to make thefollow-on track interact with the polarization condition of the beam ina different way than with the area surrounding the track. Changes in thedirection of polarization of the beam can then be converted intointensity differences with the aid of a polarization sensitive element.It is also possible to employ a follow-on track which under theinfluence of an incident beam starts to emit radiation in a manner whichdiffers from its surrounding area. The emission of radiation by thefollow-on track may be based on a fluorescence mechanism.

The follow-on track can be provided on the record carrier body inaccordance with different methods, depending on the nature ofinformation storage in the final record carrier. For example, aphoto-resist may be coated onto the disk-shaped record carrier body.This coating may be exposed to continuous radiation, the carrier body,for example, being also subjected to a radial displacement in additionto a rotation relative to the radiation source. Thus, a spiral track isexposed. Depending on the type of photo-resist, either the exposed orthe non-exposed parts will disappear upon development, so that thesubstrate, for example a reflecting layer, appears which layer can beetched away or can be rendered absorbent.

For the provision of the follow-on track use can also be made ofdifferent information storage techniques. For example, a layer of amagneto-optical or photochromic material can be spirally andcontinuously exposed with a high-power radiation beam, so that thepolarizing properties or the color properties of the layer are changed.

Generally, the record carrier body is then exposed twice. First of all acontinuous follow-on track is provided, for example, during themanufacture of the record carrier body. The information is recorded, forexample by the user himself, by intermittently exposing the recordcarrier body in accordance with the information.

The drawing shows an embodiment of a device according to the inventionwhich permits both writing and reading of the information.

The reflecting disk-shaped record carrier body 1, which is provided witha follow-on track, is rotated about a shaft 2 by a motor 3, which bymeans of a slide 4 is movable in a radial direction. A source 5, forexample a laser, emits a beam 20, of which for simplicity only one rayis shown. Included in the radiation path from the source 5 to the recordcarrier body, is an electro-optical modulator 6. Said modulator iscontrolled by a signal applied to the terminals 7, 7' and ensures thatat certain instants and during certain periods, in accordance with thesignal representing the information, a radiation spot is imaged onto theradiation-sensitive layer of the record carrier body.

The modulated beam 20 is reflected by a semi-transparent mirror 9 to aphase grating 11. This phase grating forms three secondary beams fromthe beam 20, viz. one zero-order beam, beam a, and two first-orderbeams, beams b and c. Radiation source 10, for example a laser, emits abeam 30. Said beam passes through the semi-transparent mirror 9 and,like the write beam 20, it is diffracted into different orders.

When writing on the record carrier body, the beam 30 is interrupted, forexample, by closing aperture 16. The beam a is then a write beam. Forreading purposes aperture 8 is closed and aperture 16 is open so thatbeam a then forms the read beam.

A lens 12 forms an image 11' of the grating 11, for example, in thefocal plane of a lens 15. The two radiation spots produced by thefirst-order beams b and c are projected onto the edges of the follow-ontrack during writing and onto the edges of the information track duringreading. The central radiation spot, formed by the zero-order beam isprojected in the center of the follow-on track or the information track,respectively. Especially during writing care is taken that the power ofthe first-order beams is low, so as to prevent writing by these beams.

The beams reflected by the record carrier body are reflected via arotatable mirror 14 and a semi-transparent mirror 13 to theradiation-sensitive detection system, comprised of the detectors 17, 18and 19.

Detector 17 is the high-frequency information detector which duringreading supplies a signal which is representative of to the storedinformation. By comparing the signals supplied by the detectors 18 and19, an indication can be obtained as to the positions of the radiationspots, and thus of the read and write beams, relative to the informationtrack, and the follow-on track respectively. The signals supplied by thedetectors 18 and 19 can be electronically processed into a controlsignal by means of which said positions can be corrected, for example,by rotating the mirror 14.

By making the chief rays of the beams b and c impinge on the recordcarrier body at an acute angle, and by splitting one of the detectors 18or 19 into two sub-detectors, the position of the plane of the trackportion to be read relative to the detection system can be determined asdescribed in U.S. Pat. No. 3,876,842.

An alternative solution for determining the position of the plane of thetrack portion to be read relative to the detection system is describedin U.S. Pat. No. 3,876,841. By including the same imaging element in theradiation path between the radiation source and the record carrier bodyand in the radiation path between the record carrier body and thedetection system, the deviation between the actual position of the planeof the track and the desired position of said plane can be detectedwithout using the information stored in the record carrier.

The device according to the Figure, in which three radiation spots areformed on the record carrier body and the record carrier respectivelyboth of the write source and of the read source respectively, is apreferred embodiment of the device according to the invention. It isalso possible to form only one image of the radiation source, whichsupplies the write energy, onto the record carrier body and to determinethe position of said image with the first-order sub-beams, emerging fromthe radiation source which produces the read beam. The zero-order beamof this source is then interrupted.

The type of radiation sources used for writing and reading respectively,is determined by the type of material in which the information isstored. In some cases it suffices to use a single radiation source 10for writing and reading. The path of the beam 30a then includes anelement, which affects the character of the radiation and whichdiscriminates the write beam and the read beam from each other. Forexample, if a magneto-optical material is used as a storage material,the source 10 may be a high-power laser source whose radiation duringwriting is directly incident on the record carrier body and whichilluminates the record carrier during reading via a polarizer (21),which reduces the radiation intensity.

The method of position detection of the write beam described withreference to the Figure is only one of the possibilities. The methods ofdetermining the position of a read beam relative to an information trackon a record carrier which are described in previous Patent Applicationscan also be used for writing on a record carrier body previded with afollow-on track. For example, in analogy with what is described in U.S.Pat. No. 3,833,769, a grating-shaped part of the record carrier body canbe imaged onto a radiation-sensitive detector disposed behind a grating.

If the follow-on track is a moulded groove track this track can also befollowed with a radiation spot which is greater than the width of saidtrack, as is described in U.S. Pat. No. 3,956,582.

If writing is effected on a material such that the recorded informationcan be read after a time interval of the order of the duration of onerevolution of the record carrier body, or shorter, subsequent towriting, for example, a magneto-optic or a photo-chromic material, itsuffices according to the invention if the follow-on track extends overone or several circles, or quasi-circles in the case of a spiral track.When writing information in an n^(th) track circle, or quasi-trackcircle, the information written on the (n-1)^(th) track circle, orquasi-track circle, may then be used as a follow-on track. In thewrite/read device care should then be taken that the projections of theradiation sources, which supply the write beam and the read beamrespectively, have shifted radially by one track width.

According to the invention, the follow-on track provided by themanufacturer of the record carrier body, which track extends over one orseveral circles or quasi-circles can be used for storing data which areuseful in the write-operation. In this respect a test pattern might beconceived by means of which the write and/or read device can be tested.It is also possible to store data about the record carrier body itselfor a factory name in said part of the follow-on track.

In the case of a spiral follow-on track, a spiral may be selected havinga pitch which initially is comparatively great and which graduallydecreases so that after one or several revolutions over the recordcarrier a lower, constant pitch is attained. At the beginning of thewrite-operation this will facilitate the positioning of the write beamrelative to the record carrier body.

What is claimed is:
 1. An apparatus for writing information with a writebeam of radiation on a disk-shaped record carrier body having aradiation sensitive layer and a continuous, generally circulardiffractive follow-on track extending about the center of saiddisk-shaped record carrier body, said apparatus comprising means forprojecting said write beam onto said radiation sensitive layer so as towrite information thereon upon relative movement between said carrierbody and said write beam, and means for guiding said write beam duringrecording of said information, said guiding means including means forforming a spot of radiation of a predetermined size on said follow-ontrack, said follow-on track being configured to diffract radiation ofsaid spot incident thereon when scanned with said spot and having awidth which is smaller than the dimension of said spot in the widthdirection so that the intensity distribution of radiation coming fromsaid record carrier body varies with movement of said spot relative tothe center of said follow-on track in a direction transverse to thetrack direction due to said diffraction so as to enable the position ofsaid spot relative to said follow-on track to be determined, and meansresponsive to said radiation coming from said record carrier body forcontrolling the position of said write beam during writing of theinformation on said radiation sensitive layer.
 2. The apparatusaccording to claim 1 wherein the surface of said carrier body isreflective so that the diffracted radiation of said spot is reflectedback from the record carrier body.
 3. The apparatus according to claim 1including a plurality of said circular follow-on tracks which defineturns of a spiral follow-on track extending across the surface of saidcarrier body.
 4. The apparatus according to claim 1 wherein saidfollow-on track is a groove formed in said record carrier body.
 5. Theapparatus according to claim 1, 2, or 4 wherein said follow-on trackcontains prerecorded data and includes means for reading saidprerecorded data.
 6. The apparatus according to claim 1, 2, 3 or 4wherein said means for guiding includes at least one radiation sensitivedetector positioned in the path of said radiation coming from saidrecord carrier body, said detector supplying an electrical signalindicative of the intensity of said radiation incident thereon.
 7. Theapparatus according to claim 1, 2, 3 or 4 including means for modulatingsaid write beam in accordance with information to be recorded and meansfor rotating said carrier body about the center thereof so that agenerally circular information track is recorded in said radiationsensitive layer upon rotation of said record carrier body.
 8. Anapparatus according to claim 6, wherein said guide means includes meansfor moving said write beam in a direction transverse to the direction ofsaid follow-on track in response to said electrical signal.
 9. Theapparatus according to claim 3 wherein said spiral follow-on trackcontains prerecorded data and includes means for reading saidprerecorded data.
 10. An apparatus for writing information with a writebeam of radiation on a record carrier body having a radiation sensitivelayer and a diffractive follow-on track in the form of an elongatedgroove formed in said record carrier body, said apparatus comprisingmeans for projecting said write beam onto said radiation sensitive layerso as to write information thereon upon relative movement between saidcarrier body and said write beam, and means for guiding said write beamduring recording of said information, said guiding means including meansfor forming a spot of radiation of a predetermined size on said groove,said groove being configured to diffract radiation of said spot incidentthereon when scanned with said spot and having a width which is smallerthan the dimension of said spot in the width direction so that theintensity distribution of radiation coming from said record carrier bodyvaries with movement of said spot relative to the center of said groovein a direction transverse to the longitudinal direction of said groovedue to said diffraction so as to enable the position of said spotrelative to said groove to be determined, and means responsive to saidradiation coming from said record carrier body for controlling theposition of said write beam during writing of the information on saidradiation sensitive layer.
 11. A record carrier body for recordingthereon information with a write beam of radiation, said record carrierbody having a radiation-sensitive layer on which the information to berecorded is written with the write beam and a diffractive follow-ontrack in the form of an elongated groove formed in said record carrierbody for guiding the write beam during recording of the information,said groove being configured to diffract radiation incident thereon whenscanned with a spot of radiation of a predetermined size and having awidth which is smaller than the dimension of the spot in the widthdirection so that the intensity distribution of the radiation comingfrom the record carrier body varies with movement of the spot relativeto the center of said groove due to said diffraction so as to enable theposition of the spot relative to said groove to be determined.